Evaporable foam casting, or lost foam casting, is employed to cast metal parts, and has particular use in casting parts having a complex configuration. In the typical evaporable foam casting process, a polymeric foam pattern is formed having a contour identical to the part to be cast. The pattern is positioned in a molten flask and the space around the pattern, as well as any cavities in the pattern, are filled with an unbonded flowable material, such as sand. When the molten metal contacts the polymeric pattern, the pattern will vaporize and the vapor will be entrapped within the interstices of the sand, while the molten metal occupies the void created by vaporization of the foam. The result is a cast metal part that is identical in configuration to the foam pattern. The evaporable foam casting process also has an advantage in that it uses unbonded sand which is easily recyclable and is considered environmentally friendly.
In the typical process for producing the polymeric foam patterns, a pair of aluminum dies are mounted within a mold and define a die cavity. Beads of the polymeric material, such as polystyrene or polymethylmethacrylate, are fed into the die cavity in an air stream and are heated in the die cavity by an external steam chest to thereby expand and fuse the beads and provide the foam pattern.
When casting articles of complex configuration, such as the engine block of an internal combustion engine, the polymeric foam pattern may consist of several pattern sections which are glued together along parting lines to form the pattern. Each pattern section is separately produced using a pair of aluminum dies and the aluminum dies are formed by machining a billet of aluminum to provide the contoured working surface of the die. In addition, the outer surface of the die is also machined to achieve a substantially uniform thickness for the die to provide uniform heat transfer. Because of the extensive machining operations that are required, the time and cost for producing the dies is substantial.
Various types of layered rapid profiling have been used in the past to produce three-dimensional models or images. In a typical laminated object manufacturing (LOM) system, a paper sheet coated with a heat sensitive binder, such as wax, on its undersurface is fed to a working area, where a laser beam operated by a CAD program is utilized to cut a desired configuration or pattern in the sheet. In addition, certain portions of the sheet between the cut pattern and the margin of the sheet are cross-hatched by the laser beam to permit subsequently removal. A second sheet of the wax coated paper is then applied over the first sheet and bonded to the first sheet through the use of a heated roller. The laser beam is then operated to cut to the depth of one layer of the sheet material and create the desired pattern in the second sheet. This process is repeated until the desired thickness is obtained and after removal of the cross-hatched areas a three-dimensional model is obtained. Models of this type have been used primarily to facilitate visual analysis of objects of complex configuration.